Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$130.56	9.221%	$142.5989	$142.60	$142.60	$142.60
Purchase #2	$110.96	7.541%	$119.3275	$119.33	$119.35	$119.30
Purchase #3	$80.96	11.286%	$90.0971	$90.10	$90.10	$90.10
Purchase #4	$166.71	9.586%	$182.6908	$182.69	$182.70	$182.70
Purchase #5	$78.63	12.139%	$88.1749	$88.17	$88.15	$88.20
Purchase #6	$58.81	11.217%	$65.4067	$65.41	$65.40	$65.40
Purchase #7	$129.92	10.426%	$143.4655	$143.47	$143.45	$143.50
7 purchase totals =	$756.55		$831.7614	$831.77	$831.75	$831.80